This invention relates to insulating fabrics which provide thermal protection of 2800.degree. F. (1538.degree. C.). The invention is more particularly concerned with sheath-core yarns, composed of synthetic fibers, which are useful in preparing safety garments.
U.S. Pat. No. 4,015,038, dated Mar. 29, 1977, discloses the use in dryer belts of yarns comprising textile fibers of polyethylene terephthalate or polyhexamethylene adipamide (nylon 6--6), braided over a core bundle of fiberglass (multiple glass fibers). After weaving into a belt, the yarns are coated with a resin composition capable of withstanding temperatures from about 100.degree. F. to 300.degree. F. without substantial degradation.
Safety garments have been prepared from yarns consisting of aramid fibers. As disclosed in DuPont NOMEX.RTM. aramid Bulletin N-236 dated October 1969, aramid fibers are similar to nylon 6--6 fibers in appearance and in resistance to flexing and abrasion. However, at 482.degree. F. (250.degree. C.), the melting point of nylon 6--6, these aramid fibers have a breaking strength equivalent to 60% of the value of room temperature. Aramid fibers do not melt but degradation begins to occur at temperatures above 700.degree. F. (371.degree. C.). KEVLAR.RTM. aramid fibers are similar to NOMEX.RTM. aramid fibers in the above respects; they are characterized by their remarkably high strength. KEVLAR.RTM. 29 aramid fibers have tensile strengths at 100.degree. F. (38.degree. C.) of over 20 gm/denier.
Industrial insulation has been prepared from continuous filaments of an amorphous silica product having the thermal performance of a refractory material. As disclosed in Hitco Product Data Bulletin "Engineering Data" dated October 1978, REFRASIL.RTM. textiles contain a minimum of 96% silica and a typical analysis is as follows:
______________________________________ SiO.sub.2 97.9% Fe.sub.2 O.sub.3 0.017% TiO.sub.2 0.55% ZrO.sub.2 0.017% Al.sub.2 O.sub.3 0.29% SrO 0.021% MgO 0.13% CuO trace B.sub.2 O.sub.3 0.41% NiO trace CaO 0.71% Cr.sub.2 O.sub.3 trace ______________________________________
The filaments will not melt or vaporize until temperatures exceed 3100.degree. F. (1704.degree. C.). Coatings have been used to improve their resistance to abrasion but further improvement is needed for use in safety garments.